Temperature compensated magnetron anode structure having alternate segments of differing thermal expansion coefficient



Nov. 29, 1966 J. WHITMORE ,28 37 MAG ANODE TEMPERATURE COMIEN ED NETRON STRUCTURE HAVI ALTERNATE SE NTS OF DIFFERING THERMAL EXP ION COEFFICIENT Filed April 29, 1963 EDWARD J. IT RE,

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BY 152M; 7 7 Ne AGENT.

United States Patent 3,289,037 TEMPERATURE COMPENSATED MAGNETRON ANODE STRUCTURE HAVING ALTERNATE SEGMENTS 0F DIFFERING THERMAL EX- PANSION COEFFICIENT Edward J. Whitmore, Williamsport, Pa., assignor, by mesne assignments, to Litton Industries, Inc., Beverly Hills, Calif., a corporation of Delaware Filed Apr. 29, 1963, Ser. No. 276,320 5 Claims. (Cl. 315-3955) This invention relates to multi-cavity anode structures for magnetrons. More particularly, it is concerned with temperature compensated magnetron anodes of the strapped type.

The frequency of the oscillations produced by a multicavity magnetron is determined by the resonant frequency of the cavities. The frequency at which a cavity resonates depends on the inductive and capacitive effects of the conductive elements of the anode structure which define the cavity. Changes in the size of the cavities caused by expansion and contraction of the anode structure with variations in temperature alter the inductance and capacitance in the cavities thus changing the operat ing frequency of the magnetron.

Various arrangements have been employed in magnetrons in order to compensate for changes in the resonant frequency of the cavities with variations in temperature and thus stabilize the operating frequency of the magnetron. For example, it is known to place tuning members within the evacuated chamber containing the anode which may be moved with respect to the cavities to adjust the capacitance or inductance and maintain the cavities tuned to the desired frequency. In some devices portions of the mechanism for accomplishing this function pass to the exterior of the chamber as through a flexible bellows arrangement to be actuated manually or by an automatic apparatus responsive to the temperature of the magnetron. In some devices the mechanism for moving the tuning members is completely within the evacuated chamber and includes a temperature responsive element which moves the tuning members. Intricate structures have also been devised in which elements of the structure are arranged so that the expansion of one is off-set in some manner by the expansion of another and theconfiguration of the cavity is. maintained relatively stable over a range of temperatures.

It is an object of the present invention to provide an improved means for compensating for the effects of temperature variations on magnetron anode structures.

It is a further object of the invention to provide an improved anode structure for magnetrons in which the resonant frequency of the cavities is relatively stable despite variations in temperature.

It is a more specific object of the invention to provide an improved anode structure for magnetrons in which changes caused by temperature variations are automatically compensated for by the elements of the anode structure.

Briefly, in accordance with the foregoing objects of the invention a strapped anode structure is provided in which a plurality of anode segments or vanes extend radially inward from an annular block toward a central cathode space. Alternate segments are of a material which has a high coefficient of thermal expansion, and the intervening segments are of a material which has a low coeflicient of thermal expansion. A first conductive ring or annular strap is positioned adjacent to the inner edges of the segments and is connected to the alternate segment of higher coefficient of thermal expansion. A second ring of larger diameter than the first ring is positioned adjacent to and concentric with the first ring and is connected to the intervening segments.

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As the temperature of the anode structure according to the invention increases, the elements of the structure expand thus enlarging the size of the resonant cavities between pairs of segments. As the size of a cavity increases, the inductance increases also, thus tending to lower the frequency at which resonance occurs. The alternate segments of higher coefficient of thermal expansion expand more than do the intervening segments of low coefficient of thermal expansion, and the spacing between the two straps is thereby increased. As the distance between the straps is increased the capacitance between them is decreased, thus tending to raise the fre quency at which resonance occurs. Compensation is thereby achieved for the tendency of the inductance to increase with increasing temperature.

Additional objects, features, and advantages of magnetron anode structures according to the invention will be apparent from the following detailed discussion and the accompanying drawings wherein:

FIG. 1 is an elevational view in cross-section of a portion of a magnetron illustrating an anode structure according to the invention taken generally along line 11 of FIG. 2, and

FIG. 2 is a plan view in cross-section taken generally along line 22 of FIG. 1.

A magnetron as illustrated in the drawings embodying an anode structure according to the invention includes a hollow cylindrical anode block 10 providing the walls for an enclosed cylindrical chamber 11. An even numbered plurality of radially extending segments or vanes 13 are fastened at their outer edges to the inner surfaces of the anode block. The inner edges or tips 14 of the vanes terminate in spaced apart relationship adjacent to the central region of the anode structure providing space for an electron emissive cathode 15.

An upper magnet pole piece 20 is sealed in position across the upper end of the anode block providing an end space 21 between the upper ends of the anode segments and the pole piece. A lower magnet pole piece 22 is sealed across the lower end of the anode block providing a lower end space 23. The cathode passes through a bore (not shown) in the lower pole piece which is suitably sealed to allow evacuation of the chamber 11. The space between each pair of segments constitutes an open-ended resonant cavity 25. Electromagnetic energy is coupled from the magnetron through an output coupler 26 extending through the wall of the anode block and communicating with one of the resonant cavities.

A pair of conductive rings or annular straps 30 and 31 coaxial with the anode block and cathode are provided adjacent to the inner edges or tips at the upper ends of the anode segments. A similar pair of straps 32 and 33 are provided at the lower ends of the anode segments. As is well known in the magnetron art, the straps connect alternate segments together in order to restrict the magnetron to operation in only the predominant or 11' mode and suppress other modes of oscillation.

In anode structures according to the invention the alternate anode segments 13a, which constitute a first set of segments, are fabricated of a material having a high coefficient of thermal expansion, such as, for eX ample copper. The intervening segments 1317, which constitute a second set of segments, are fabricated of a material which has a low coefficient of thermal expansion, such as, for example molybdenum. The anode block 10 is of a conductive material, such as copper, which is commonly employed in magnetron anode structures.

The two pairs of concentric conductive straps 30 and 31, and 32 and 33 are mounted within recesses or notches 35 in the ends of the anode segments. The straps may be of any suitable conductive material, such as, for example copper. The inner strap 30 of the upper pair is electrically and mechanically connected to the copper segments 13a, which have a high coefilcient of thermal expansion. The recesses in the ends of the molybdenum segments 13b are of such configuration that the inner strap passes through them without making contact with the segments.

The outer strap 31 of larger diameter is mounted within the recesses in electrical and mechanical contact with the molybdenum segments 1312, which have a low coeflicient of thermal expansion. The recesses are of such configuration that the outer strap does not make contact with the copper segments.

The second pair of annular straps 32 and 33 are mounted in the lower ends of the anode segments in a manner similar to the mounting of the first pair. They are each of the same diameter as the corresponding strap of the upper pair and are concentrically arranged in the anode, The inner strap 32 is electrically and mechanically connected to the copper segments 13a and is spaced from the molybdenum segments 13b. The outer strap 33 is electrically and mechanically connected to the molybdenum segments 13b and is spaced from the copper segments 13a.

The frequency of resonance of each of the open-ended cavities 25 is determined by the inductive and capacitive effects of the elements of structure, adjoining the space constituting the cavity. As the temperature of the anode structure increases, the anode block expands increasing the size of the cavities. Primarily, this change increases the inductance of the cavities thereby decreasing the frequency at which resonance occurs.

Since the two sets of anode segments are of different materials and have different coefiicients of thermal expansion, they do not expand equal amounts upon increase in the temperature of the stucture. The molybdenum segments 13b of the second set expand less than the copper segments 13a of the first set; and, therefore, assuming identical initial length of all the segments, the tips 14 of the copper segments 13a are closer to the center of the anode than are the tips of the molybdenum segments 13b. Since the inner straps 30 and 32 are mechanically fastened to the copper segments 13a and the outer straps 31 and 33 Which encircle their associated inner strap 'are mechanically fastened to the molybdenum segments 13b, the spacing between the two straps of each pair is increased. The increase in distance between the straps decreases the capacitance between them thereby increasing the frequency at which the cavities will resonate.

Thus, in an anode structure according to the invention the increase in inductance caused by the expansion of the resonant cavities is compensated for by a decrease in capacitance caused by the increased spacing between the straps. In this way the effects of changes in temperature are minimized and the operating frequency of the magnetron is maintained relatively stable. These results are achieved by the elements of the anode structure themselves with no additional external or internal compensating mechanisms.

What is claimed is: I

1. A magnetron anode structure comprising an annular block,

, a plurality of anode segments extending radially in- Ward from said annular block,

alternate segments being fabricated of a material having a high coeflicient of thermal expansion,

the intervening segments being fabricated of a material having a low coefiicient of thermal expansion,

a first conductive ring adjacent to the inner edges of said segments connected to said alternate segments, and I t a second conductive ring of larger diameter than the first ring adjacent to said first ring and connected to the intervening segments.

2. An open-ended cylindrical anode structure comprising an annular block,

a plurality of segments extending radially inward from said annular block,

alternate segments being of a materiathaving a high coefiicient of thermal expansion,

the intervening segments being of a material having a low coeflicient of thermal expansion,

the inner edges of said segments bounding a central cathode space, and

a pair of metallic rings at each end of said segments,

the smaller one of said rings of each of said pairs being adjacent to the inner edges of said segments and connected to said alternate segments,

the larger one of said rings of each of said pairs being adjacent to and concentric with the smaller ring and connected to the intervening segments.

3. An annular anode structure comprising a plurality of radial segments providing a plurality of resonant cavities therebetween,

a cathode space located centrally of the inner tips of said segments, 7

alternate segments constituting a first set of segments and the intervening segments constituting a second set of segments, V

the segments of said first set having a high coefiicient of thermal expansion,

the segments of said second set having a low coeificient of thermal expansion,

a first annular metal strap recessed into one end of said segments adjacent to the tips thereof makingv electrical contact with the segments of said first set.

and passing through recesses and being separated electrically from the segments of said second set, and

a second annular metal strap of larger diameter than said first strap recessed into the one end of said segments encircling and concentric with said first strap making electrical contact with the segments of said second set and passing through recesses and being separated electrically from the segments of said first set.

4. A magnetron anode structure comprising a cylindrical anode block,

a plurality of segments extending radially inward from said block and providing a resonant cavity between each pair thereof,

the inner tips of saidsegments being spaced apart and providing a circular cathode space centrally of the anode block,

alternate segments constituting a first set of segments and having a high coefiicient of thermal expansion,

the intervening segments constituting a second set of segments and having a low coeflicient of thermal expansion,

a first annular metal strap at each end of said segments located in recesses in the ends of the segments adjacent to-the tips thereof and making electrical contact with the segments of said first set and being separated electrically from the segments of said second set, and r a second annular metal strap of larger diameter than said first strap at each end of said segments located in said recesses concentric with said first strap and making electrical contact with the segments of said second set and being separated electrically from the segments of said first set.

5. A magnetron anode structure comprising a cylindrical anode block,

I a plurality of segments extending radially inward from said block and providing a resonant cavity between each pair thereof,

the inner tips of said segments being spaced apart and providing a circular cathode space centrally of the said first strap recessed in each end of the seganode block, ments adjacent to and coaxial with the first strap alternate segments being fabricated of copper, making electrical and mechanical connection with the intervening segments being fabricated of molybthe molybdenum segments and passing through -redenum. 5 cesses and being separated electrically from the copa first annular metal strap recessed in each end of the per segments.

segments adjacent to the tips thereof making electrical and mechanical connection with the copper No references cited.

segments and passing through recesses and being separated electrically from the molybdenum seg- 10 HERMAN KARL SAALBACHPrmm'y Exammermalts, and E. LIEBERMAN, Assistant Examiner. a second annular metal strap of larger diameter than 

1. A MAGNETRON ANODE STRUCTURE COMPRISING AN ANNULAR BLOCK, A PLURALITY OF ANODE SEGMENTS EXTENDING RADIALLY INWARD FROM SAID ANNULAR BLOCK, ALTERNATE SEGMENTS BEING FABRICATED OF A MATERIAL HAVING A HIGH COEFFICIENT OF THERMAL EXPANSION, THE INTERVENING SEGMENTS BEING FABRICATED OF A MATERAIL HAVING A LOW COEFFICIENT OF THERMAL EXPANSION, A FIRST CONDUCTIOVE RING ADJACENT TO THE INNER EDGES OF SAID SEGMENTS CONNECTED TO SAID ALTERNATE SEGMENTS, AND A SECOND CONDUCTIVE RING OF LARGER DIAMETER THAN THE FIRST RING ADJACENT TO SAID FIRST RING AND CONNECTED TO THE INTERVENING SEGMENTS. 